RAIN GARDENS
~managing roof runoff in your backyard~
Before
After
Before
Portland Water District
After
http://clean-water.uwex.edu/pubs/raingarden/gardens.pdf
Purpose: Rain gardens are attractive and functional landscaped areas that are designed to capture
and filter stormwater from roofs, driveways, and other hard surfaces. They collect water in bowlshaped, vegetated areas, and allow it to slowly soak into the ground. This reduces the potential for
erosion and minimizes the amount of pollutants flowing from your lawn into a storm drain, and
eventually into our streams and lakes.
Installation: Rain gardens can vary in size, but are most
effective when built to 20-30% of the drainage area. Rain
gardens for single-family homes will typically range from 150
to 300 square feet, but even a smaller one will help reduce
water pollution problems.
™ The garden should be bowl-shaped, with the lowest point of
the garden no more than 6” below the surrounding land.
™ The sides should be gently sloping towards the center to
prevent sudden drop-offs that could lead to erosion
problems or walking hazards.
™ Rain gardens are often placed in a preexisting or created
depression within a lawn, or in a location that receives roof
runoff from a downspout.
™ To avoid flooding improperly sealed foundations, build your
rain garden 10’ away from existing structures, and direct
water into the garden with a grassy swale, French drain,
gutter extension or other device.
Rain gardens can be placed in sunny or shady regions of your lawn, but plants should be chosen
accordingly, with the lowest point planted with wet tolerant species, the sides closest to the center
planted with moist tolerant species, and the edges of the rain garden should be planted with subxeric (moist to dry) or xeric (dry) tolerant plants. It is also important to check the permeability of
your soil. Sandy soils only need compost added, but clay soils should be replaced with a mix (5060% sand, 20-30% topsoil, 20-30% compost). After construction of the garden is complete, the
entire area should be covered with a thick layer of mulch, preferably Erosion Control Mix.
Materials: Replacement Soil mixes and Erosion Control Mix are available from local garden
centers. Native plants can be purchased from your local nursery. Please see Native Plant Lists from
this series for plant descriptions based on specific sun and soil conditions.
Maintenance: Overall, once plants mature, the maintenance of a rain garden is very low.
Watering is important during the first growing season, and some weeding is necessary after
planting. As the garden matures, some of the perennials may need to be divided if plantings become
too crowded.
Part of the Conservation Practices for Homeowners Factsheet Series, available at:
Maine DEP (800.452.1942); http://www.maine.gov/dep/blwq/docwatershed/materials.htm
Portland Water District (207.774.5961); http://www.pwd.org/news/publications.php
May 2006 DEPLW0784